An information processing system connecting a large number of widely distributed computers by a network is known. Such an information processing system is also hereinafter simply described as a widely distributed information processing system. For example, a machine to machine (M2M) system and an internet of things (IoT) are given as representatives of a widely distributed information processing system. A hierarchical structure is widely used in a widely distributed information processing system. For example, a server mainly performing information processing in a system is placed in a cloud connected to the Internet. On the other hand, a terminal and a device using the server are placed at a location physically remote from the server, such as a building or a site of a system user. A relay device relaying data is placed between the terminal and the device, and the server. A relay device installed at a location relatively close to a terminal and a device will be hereinafter touched on. For example, a relay device communicates with a terminal and a device by using a local area network (LAN), a personal area network (PAN), a home area network (HAN), and the like. Further, for example, a relay device is connected to the Internet by using a wide area network (WAN) and communicates with a server. Further, a relay device may not only relay data but also perform primary processing on a request and the like from a terminal or a device.
An example of a widely distributed information processing system is described in PTL 1. A related art described in PTL 1 provides redundancy for a relay device in a widely distributed information processing system. The related art associates an auxiliary relay device with a main relay device. Then, the auxiliary relay device periodically receives information indicating a state of a session related to user equipment, from the main relay device. Then, the auxiliary relay device restores a session being down, in response to a failure of the main relay device, and restores a session state of the user equipment.